This is my first turntable I have designed, and am looking for input on this drive/bearing system.
The motor (the square at the bottom) is a direct drive motor, but to reduce rumble/noise, I want to have a magnet-coupled drive as seen here. The magnets alternate N and S facing up. I am worried mainly about the magnet proximity to the cartridge. Here it is 2.67 inches from the closest magnet to the top of the platter. Would this be a problem? I was thinking of adding MU-metal shielding. Would that be effective?
The bearing is teflon with a triangle hole and the spindle sits in it so that it contacts 3 sides, and the vertical support is taken care of a flare on the spindle that contacts the edge of the hole. This was inspired by the Well Tempered Labs bearing design. The bearing is light colored cylinder near the middle.
Finally, just another idea, also inspired by Well Tempered Labs. The half of the magnet coupler attached to the platter spindle and bearing are in a 'cup' that is filled with a viscous fluid for dampening. Not to viscous, since I don't want fluid friction to be an issue.
Feedback?
The motor (the square at the bottom) is a direct drive motor, but to reduce rumble/noise, I want to have a magnet-coupled drive as seen here. The magnets alternate N and S facing up. I am worried mainly about the magnet proximity to the cartridge. Here it is 2.67 inches from the closest magnet to the top of the platter. Would this be a problem? I was thinking of adding MU-metal shielding. Would that be effective?
The bearing is teflon with a triangle hole and the spindle sits in it so that it contacts 3 sides, and the vertical support is taken care of a flare on the spindle that contacts the edge of the hole. This was inspired by the Well Tempered Labs bearing design. The bearing is light colored cylinder near the middle.
Finally, just another idea, also inspired by Well Tempered Labs. The half of the magnet coupler attached to the platter spindle and bearing are in a 'cup' that is filled with a viscous fluid for dampening. Not to viscous, since I don't want fluid friction to be an issue.
Feedback?
Attachments
it goes without saying that the plinth is not here. The magnet drive is not levitating, this is just what it looks like completely exposed. the bearing takes the weight of the platter.
if the magnet drive is not levitating then why use magnets?
if you dont want to transfer noise from the DD drive then couple with rubber bushing.
as for 'viscous fluid' for the bearing i would use a good plastics grade grease instead.
have you considered using a plain bearing and a rotary shaft seal, that way the fluid will stay put and you get a much larger area for the fluid to 'cushion' the bearing from the shaft.
if you dont want to transfer noise from the DD drive then couple with rubber bushing.
as for 'viscous fluid' for the bearing i would use a good plastics grade grease instead.
have you considered using a plain bearing and a rotary shaft seal, that way the fluid will stay put and you get a much larger area for the fluid to 'cushion' the bearing from the shaft.
The magnet is there to drive the platter in order not to have physical contact with the platter and main bearing. Magnetic levitation in turntable design is a bad idea. Since magnetic force is a compliant system, not rigid, so there will always be vertical movement in microscopic level and it will affect VTA for the cartridge. However, using magnet to lessen the mass of the platter is a good idea as long as the magnetic field is well shielded.
I get what Dumbledog is doing but I honestly think the idea is misguided. He's assuming there's "rumble/noise" in a DD motor. Typical DD motor are brushless so there's no contact with the bearing, it's the purest form of magnetic drive, which itself have compliance built in, the magnetic force can be soft or hard depending on torque and servo design. Whatever the flaws of the DD system, noise is NOT one of them. It's a misconception repeated ad nauseam. The platter and motor shares the same bearing, hence DIRECT drive. What Dumbledog is doing is just adding an extra layer of compliance and isolation to the direct drive motor. But at the same time he's compromising the quality of the bearing as it has to run dry and increasing contact area at the thrust plate area or the lack of a thrust plate. The triangular hole now has THREE points of contact, instead of the traditional single bearing ball on a thrust plate, and running DRY. If Dumbledog is savvy with machining, another suggestion is to disassemble the DD motor and to improve its bearing or to machine a new bearing and add fluid damping on the circumference of the motor. You just have to imagine the platter being part of the motor.
This idea of magnetic drive has been done using belt-drive motors in designs like the EAR Diskmaster, Clearaudio Master Innovation and Statement, various Transrotor TMD models. But they all use belt drive for the lower part. What they're recreating, in essence, is just another more isolated version of the DD motor. The beauty of a DD turntable is its simplicity because it only has ONE single moving part, the bearing. Noise is a function of the bearing and as long as the maker pay attention to the quality of the bearing just like any other drive system, it will be free of noise. Of course, the bane of the design is to make it spin at 33rpm smoothly with no cogging. But that's a different topic entirely.
Here's a fun idea. If you can build this system on to a rack system having enough space below the upper assembly, then you can place a whole direct drive turntable underneath it, put a the attracting magnets on its platter and let it drive the upper deck. This way it can be versatile and test different kinds of DD tables as a motor unit without taking out the actual motor. So it's one active turntable driving another passive turntable in totem pole style! It should be fun. And if you have a collection of DD turntables, you can have a blast! At one point I had 30 DD turntables and I wish I had a rig like that to test the different "flavors" of these tables!
Some example of double-deckers:
The EAR Diskmaster driven by a gear belt! The design is being forced to use "angular contact bearing" which I believe is a compromise.
Notice the gap between bottom and top assemblies.
Clearaudio Master Innovation
Transrotor TMD (Transrotor Magnetic Drive) designs, by far the most elegant of this genre.
Three belt version.
http://www.hifireview.com.hk/d/site...blic/JR Transrotor Rondino nero FMD#311-2.jpg
http://www.hifireview.com.hk/d/site...blic/JR Transrotor Rondino nero FMD#311-3.jpg
The EAR Diskmaster driven by a gear belt! The design is being forced to use "angular contact bearing" which I believe is a compromise.
An externally hosted image should be here but it was not working when we last tested it.
Notice the gap between bottom and top assemblies.
Clearaudio Master Innovation
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Transrotor TMD (Transrotor Magnetic Drive) designs, by far the most elegant of this genre.
An externally hosted image should be here but it was not working when we last tested it.
Three belt version.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
http://www.hifireview.com.hk/d/site...blic/JR Transrotor Rondino nero FMD#311-2.jpg
http://www.hifireview.com.hk/d/site...blic/JR Transrotor Rondino nero FMD#311-3.jpg
I'm not a fan of the Garrards and the like, but the whole idea is to have 'instantaneous torque' that has as close to zero 'sag' as is possible. When the groove slaps the stylus sideways, the stability of the torque in the microsecond range of response.. becomes the key point. Mass and magnetic drive fixes some of the issue, but not all if it.
which is why we have those very pretty turntables for $100K, that could have done it right, for..er well..simply... by moving in a different direction. Not a bigger hammer, but the correct one, instead.
As for maintaining instantaneous torque, over the long term, under extremely dynamic conditions....Rim (I'm meaning 'idler wheel') drive does that pretty dang well. It gets one of the fundamentals of how the ear works - it gets that right. Which goes a long long way toward realism in reproduced sound.
Tim's EAR turntable might be a bit, er... awkward, but it leans in the direction of the idler drive, which is not a bad thing.
If you can get some part of the rotating drive system to hit 2000 rpm, that's the Rpm where the 'win' begins.
which is why we have those very pretty turntables for $100K, that could have done it right, for..er well..simply... by moving in a different direction. Not a bigger hammer, but the correct one, instead.
As for maintaining instantaneous torque, over the long term, under extremely dynamic conditions....Rim (I'm meaning 'idler wheel') drive does that pretty dang well. It gets one of the fundamentals of how the ear works - it gets that right. Which goes a long long way toward realism in reproduced sound.
Tim's EAR turntable might be a bit, er... awkward, but it leans in the direction of the idler drive, which is not a bad thing.
If you can get some part of the rotating drive system to hit 2000 rpm, that's the Rpm where the 'win' begins.
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When I saw your pictures, I thought of the EAR Disk Master where they have no problem with the magnets, I think you are exaggerating the magnets influence its impact on the cartridge. I have done quite unscientific tests after I listened to the disk master and found that magnetics effect disappears quickly since many believe that the sound will be worse but the cartridges are full of magnets.
Well I really like your idea, I was close to buying Disk Master after hearing it but the price stopped me, but a DIY version would certainly be fun to build.
The bearing you have drawn has Dr. Forsell used on a turntable, an article in a Swedish audio magazine where you could buy some parts and other parts did you yourself.
That which I could point out is that the shaft can be made longer at your sketch and let the bearing to be longer or two pieces.
Anders
Well I really like your idea, I was close to buying Disk Master after hearing it but the price stopped me, but a DIY version would certainly be fun to build.
The bearing you have drawn has Dr. Forsell used on a turntable, an article in a Swedish audio magazine where you could buy some parts and other parts did you yourself.
That which I could point out is that the shaft can be made longer at your sketch and let the bearing to be longer or two pieces.
Anders
The teflon bearing isn't running dry, though. The magnet assembly and bearing are both submerged in lubricant that would also supply fluid dampening. The bearing was designed to take care of the need for a thrust plate, but to add one should be possible if that is a better way of doing it.
The magnet assembly is not the contact point where the pressure of the mass is loaded. The edges of the triangular hole are the contact points where they deal with the load and if you place fluid there, it will leak out. And the bearing shaft is also not submerge in oil either. There are also no azimuth (or axial?) support other than the magnetic attraction at the bottom, not rigid enough. Too much wriggle room. If you a better method, I want to see it. There's really no better or simpler way of a bearing system using a shaft in a hole with the single point of a ball against a thrust plate. Why reinvent the wheel?
Another way to approach it is to borrow the TMD and EAR concepts and then use a gear belt or non-compliant belt (no slippage, no stretching, no smearing) to drive the magnet assembly but instead of driving it underneath, drive it side by side and the DD motor use a pulley the same diameter as the magnet assembly then it's one to one ratio. This way you can still make a traditional bearing for the platter AND using a DD motor running at 33rpm. Study the Transrotor approach and the possibilities are limitless. The bearing for the magnet assembly will be some kind of ring bearing or angular contact bearing. You will end up with TWO bearings, one for the platter, one for the magnet assembly, neither touch each other but one is driven by the other's attracting magnetic force.
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I can't edit the drawing but just imagine the motor pulley is the same size as the magnet assembly so a DD motor can drive it one to one ratio at 33rpm.
An externally hosted image should be here but it was not working when we last tested it.
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Another drawing with a different approach from Transrotor the FMD system from a website.
An externally hosted image should be here but it was not working when we last tested it.
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I see a lot of drawings and pictures that appear to have been lifted from various other sites. Have any of you received permission to post these pictures here? If not these posts are in violation of international copyright law and are subject to removal.
fair use likely permits - there is no commercial use here.
this is clearly for educational and investigational purposes.
imo.
this is clearly for educational and investigational purposes.
imo.
It's html. I didn't download the pictures and then upload them onto this forum. They are all links so if you click on all the pictures, it inevitably goes back to the original site. Check the addresses. I don't believe there's violation when linking pictures. Unlike many members here (or facebook), they see a picture they want to post, rip it and then upload to the forum. I ALWAYS provide a link to the source. I hate to upload pictures, such a waste of data, and html also allows non-members to see the pictures. Unless they are my own drawings but even that I still prefer to upload to tinypic or imgur so EVERYBODY can see them.
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Dumbledog:
While I am not a turntable designer, I do have some friends who are. I am fortunate to have a nice machine shop in my basement and intend to build my own turntable according to well founded principals that I read about and advice given to me over the years.
At one of the CES shows I spent about 30 min or so talking to a Clearaudio rep about their Statement turntable and had some hands on this mechanical work of art. I can say they accomplished their goal to decouple the motor drive system from the record platter by using magnetic attraction of the platters. While at the time it was a novel idea I discovered it was both a plus and a minus. When I manually spun the bottom drive platter suddenly, there was a long delay before the top platter started to move. This is much like a belt drive turntable with a very loose belt IMHO. It is this " soft " coupling between the 2 platters that I feel is not the best solution for a turntable drive system. Their system does work well but I feel it more for a selling point then a practical solution.
When I build my turntable it will have:
!. A high mass, balanced platter of between 40 to 70lbs. I will experiment with delrin, aluminum, copper in some combination.
2. A pair of neo ring magnets to lift about 75 to 90 percent of the platter weight, one at the bottom of the platter and the other in the plinth and shielded.
3. An inverted bearing using polished tungsten carbide shaft sitting at the center of gravity of the platter. I will try bronze bushing and some of the high tech plastics and see which works best.
4. A multiple motor/controller belt drive system.
Other dive systems will also work but a belt drive was proven to my satisfaction to have least amount of compromise / complication / noise. Feel free to agree or disagree with my design parameters.
While I am not a turntable designer, I do have some friends who are. I am fortunate to have a nice machine shop in my basement and intend to build my own turntable according to well founded principals that I read about and advice given to me over the years.
At one of the CES shows I spent about 30 min or so talking to a Clearaudio rep about their Statement turntable and had some hands on this mechanical work of art. I can say they accomplished their goal to decouple the motor drive system from the record platter by using magnetic attraction of the platters. While at the time it was a novel idea I discovered it was both a plus and a minus. When I manually spun the bottom drive platter suddenly, there was a long delay before the top platter started to move. This is much like a belt drive turntable with a very loose belt IMHO. It is this " soft " coupling between the 2 platters that I feel is not the best solution for a turntable drive system. Their system does work well but I feel it more for a selling point then a practical solution.
When I build my turntable it will have:
!. A high mass, balanced platter of between 40 to 70lbs. I will experiment with delrin, aluminum, copper in some combination.
2. A pair of neo ring magnets to lift about 75 to 90 percent of the platter weight, one at the bottom of the platter and the other in the plinth and shielded.
3. An inverted bearing using polished tungsten carbide shaft sitting at the center of gravity of the platter. I will try bronze bushing and some of the high tech plastics and see which works best.
4. A multiple motor/controller belt drive system.
Other dive systems will also work but a belt drive was proven to my satisfaction to have least amount of compromise / complication / noise. Feel free to agree or disagree with my design parameters.
Thank you for confirming my speculation about such designs. Once again, magnet is a compliant force just like a rubber band. But people are attracted by the non-contact novelty (One reviewer, Harry Pearson, who gave it a rave review and compared that to driving a car without the tires touching the road!). I think Clearaudio's method compromises the rigidity of bearing. I am told their magnetic bearing (top portion of the table) has no mechanic grounding so the bottom point is not touching any thrust plate so it's floating. There's no path for the energy transfer or drainage. One account says when press the platter bounces up and down, that's clearly not rigid and will affect VTA or vertical information.
Great observation.
.
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I listen to a fully mag levved deck every week at my friends house, there's no issue with vertical compliance, just make the design so the load on the mag Lev system is heavily compressed so that any difference in weight from record to record is such an inconsequential fraction of the supported weight it causes no deflection. They don't dip and Bob as they rotate.
There's also no issue with 'grounding' in the closed loop sense of the term as promoted by Linn. The bearing contact point is a source of noise, no more no less, removing it typically improves snr by 2-3db.
Mag drive on the other hand is beset with issues...
There's also no issue with 'grounding' in the closed loop sense of the term as promoted by Linn. The bearing contact point is a source of noise, no more no less, removing it typically improves snr by 2-3db.
Mag drive on the other hand is beset with issues...
Here it is with the addition of the cup for fluid. The bearing has been changed so now it is an inch tall. There shouldn't be wiggle room, assuming proper tolerances- same as a bushing being close fitting, the shaft is a close fit in the triangular hole. To remove the need for a thrust plate/bearing the shaft has a flare.
The entire cup is going to be filled with fluid, including the bearing. I understand the need for mechanical damping, and I feel that the design principles utilized by Well Tempered Labs provide this damping.
Attachments
You're right. Perhaps I was being too generalized on magnetic levitated bearing. It reminds me of airbearing tables a la Micro Seiki or Techdas et al.... No one ever seems to complain about their sound except invariably rave about how quiet the background noise is. If the layer of magnetic force or air is compressed hard enough, it should be fine. After all, many thrust plate made out of plastic material can change thickness over time too.
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